When Google indexes so many billions of web pages that it doesn’t even bother listing the number any more, it’s hard to imagine that much lies beyond its far-reaching tentacles.

Beneath, however, lies an online world that few know exists. It’s a realm of huge, untapped reserves of valuable information containing sprawling databases, hidden websites and murky forums. It’s a world where academics and researchers might find the data required to solve some of mankind’s biggest problems, but also where criminal syndicates operate, and terrorist handbooks and child pornography are freely distributed.